An arson attack at Brighton and Hove Pride caused £30,000 damage to a block of portable toilets.
The toilets, on the north side of the park near Preston Park Avenue, were deliberately set alight at about 10pm on Saturday 7 August.
Detectives from Sussex Police are trying to find the person who started the fire.
Detective Constable Katy Hartley said: “The fire was quickly dealt with by East Sussex Fire and Rescue Service and no one was injured.
“This is a serious offence and I’m keen to speak to anyone with information, particularly to a group of around five youths aged 16-20 who were seen running from the area at the time of the fire.”
Fire investigators from East Sussex Fire and Rescue have confirmed that the fire was started deliberately.
Anyone who can help solve this crime is asked to call Sussex Police on 0845 6070999.
Witnesses can also call the independent charity Crimestoppers anonymously on 0800 555111.